1. Field of the Invention
The present invention relates to a pump for supplying a cryogenic liquid coolant, and more particularly to a pump for supplying a cryogenic liquid coolant capable of maintaining an outlet port side pressure in a stable manner by exhausting vapor generated within the pump through vent holes when supplying the cryogenic liquid coolant.
2. Description of the Prior Art
As generally known in the art, a cryogenic liquid coolant is provided to a superconducting motor or generator or the like through a supply pump, while maintaining as close to a cryogenic state as possible. At this moment, since the cryogenic liquid coolant (referred to as “coolant” hereinafter) is in a state just before boiling, it has characteristics to be easily evaporated by a small temperature difference or the like during its supply process.
However, such a pump for supplying the coolant is considerably vulnerable to vapor or gas. If the gas ratio within the pump is more than about 5-10% during the supply process of the coolant, both the suction and discharge pressures by an impeller are rapidly reduced, so that the coolant may not be discharged.
In general, the coolant is introduced into an inlet port by the rotation of the impeller, and the coolant, after entering the inlet port, passes through a chamber to be discharged to an outlet port. At this moment, a portion of the coolant is evaporated to generate vapor by the temperature difference or the like within the chamber. The vapor, as shown in FIG. 1, serves as a factor to make an outlet port pressure unstable. As such, when the outlet port pressure becomes unstable, the suction and discharge operation of the coolant is not performed in a stable manner, and further a considerably big noise is generated. If such circumstances become much worse, the pumping operation should be stopped, or the pump might be damaged.
Particularly, as shown in FIG. 2, if the rotational speed of the impeller increases over a certain speed, the pressure at the outlet port cannot increase anymore due to the vapor of the coolant. This is attributed to uneven suction and discharge operations by the impeller due to the vapor, which is partially re-circulated to the inlet port by the impeller reducing the suction pressure. The vapor re-circulated to the inlet port increases as the rotational speed of the impeller increases. Consequently, as shown in FIG. 2, it can be noted that the outlet port side pressure cannot increase further over the certain rotational speed of the impeller, and the cryogenic liquid coolant cannot be properly supplied.